code: def modify_layout(layout, output_dim, axis=None, axis_name=None):
      if not axis_name or (not layout and output_dim > 1):
          return ""
      if output_dim == 1:
          return axis_name
      layout = layout or ""
      if axis < 0:
          axis = len(layout)
      return layout[:axis] + axis_name + layout[axis:]
  
imports: from functools import partial
  from nvidia.dali.pipeline import Pipeline
  import nvidia.dali.ops
  import nvidia.dali.types
  from test_utils import check_batch
  from nose_utils import raises
  import numpy
label_desc: Use image node_id 3 for calling a global function with example usage: modify_layout(layout, output_dim, axis, axis_name) and returns: unknown, str, axis_name